Reciprocating engines have machined crankshafts that rotate at high speeds, and also have pistons and connecting rods that oscillate up and down with every revolution of the machined crankshaft. These parts are referred to as the engine's rotating assembly. Machined crankshafts need to be highly engineered, so as to maximize the efficiency of the energy conversion process and also to resist shock loading issues and fatigue failure. Further, machined crankshafts need to be light and small, so as to provide fast response times and to be compact enough to fit inside of an engine block.
Crankshafts may be made by a deformation process in which the work is compressed between a pair of dies, using either impact or gradual pressure to form the part. Over time, the dies change and cause latent changes between (respective) crankshafts. As just one example, when the dies form the crankshaft, there may be a thin web left thereon where the two dies meet. The size of the thin web varies between the crankshafts, as its size is related to how much wear there is on the dies.
Engine designers specify material distribution in critical areas for ensuring that mechanical material limits of the machined crankshaft are not exceeded. For example, a pin journal of the machined crankshaft transmits energy of the piston through the web of material that joins the pin journal to the main journal. There must be enough material that is properly located in the web for preventing failure thereof. In at least some cases, the web and the pin journals have been identified as the weakest areas of the machined crankshaft. Despite the importance and potential weakness of the web and pin journals, they may be defect prone. The heated steel used to form the crankshaft is subjected to the highest flow rate and restrictions in the pin journal area, resulting in a higher likelihood of die wear in these particular areas and a higher likelihood of improper die fill. Further, the pin journals lie on a parting line where upper and lower dies join together in the forging process, resulting in misplaced material caused by the dies shifting relative to each other or the dies not closing completely.
One manufacturing method is to visually inspect each crankshaft for issues relating to improper die fill and misplaced material; however, such a method is labor intensive and subject to human error.